China reaffirms push to pressure N.Korea

China's top diplomat has reaffirmed a commitment to pressure North Korea over nuclear weapons.

US Secretary of State Rex Tillerson and China's top diplomat, Yang Jiechi, have reaffirmed their countries' commitment to exert pressure on Pyongyang over its nuclear weapons, the US State Department says.

Yang was on a two-day visit to Washington that began on Thursday. His talks were also expected to cover the sensitive US-China economic relationship after recent tit-for-tat actions that have raised fears of a trade war between the world's two largest economies.

"Both sides reaffirmed President Trump's and President Xi's commitment to keep up pressure on North Korea's illegal weapons and nuclear programs," State Department Spokeswoman Heather Nauert told a news briefing.

Nauert said Tillerson and Yang "agreed on the importance of continuing a constructive and productive relationship aimed at co-operation on mutual challenges and addressing our differences forthrightly".

Beijing and Washington share concerns about North Korea's development of nuclear missiles capable of hitting the US.

China has backed successive rounds of UN sanctions on North Korea but has been wary of US efforts to toughen these further and has been accused by US officials of not fully implementing existing UN steps.

"We expect, we hope that China will do more, because we know they can do more in terms of adhering to UN Security Council resolutions," Nauert said.